An ink jet printer for the labelling of goods with a write head, comprising a) at least one outlet opening for ink droplets at a frontal surface, b) a mechanism connected to the outlet opening, c) a pneumatic pump and d) an electrical control, and having at least one supply tank for fluid flowing through the outlet opening, such as e.g. ink, pigment or solvent, wherein the supply tank is releasably connected to the write head in a coupling area, and comprising a housing as well as a foldable bag residing in said housing, in which bag the fluid is accommodated and which is connected to the printing mechanism via an ink line, which is passed across the coupling area, the pneumatic pump is connected to the space between the housing and the bag via a compressed-air line and thus pressurizing said space with overpressure.
The invention preferably relates to such ink jet printers in the form of hand-held devices, see e.g. WO2013/120702 A1, it may also be utilized with stationary devices, see e.g. EP 1 064 153 B1. Hand-held devices are self-contained, they are provided with a voltage supply source, especially an accumulator, for example, like cordless screwdrivers. With stationary devices, voltage supply generally is done from the outside, e.g. via the regular electrical grid.
The fluid required for the printing procedure is in the supply tank. For this purpose, reference is made to WO 2013/120702A1, the disclosure of which is fully incorporated into the disclosure of the present application and in this respect is included therein. In practical operation, the supply tank is required to be quite frequently replaced, as the fluid, while being pressurized, is constantly consumed, thus depleting the supply after a certain number of pressurizing cycles. Therefore, the supply tank is formed such that it may easily be replaced. It may be released from the write head at the coupling area. When decoupling, the ink line and the compressed-air connection will be interrupted.
A supply tank having an internal bag, which receives the fluid, and a compressed-air space located between the bag and the housing of the supply tank have the advantage that hydraulic pressure required for the pressurizing procedure is or may be achieved by way of pneumatic pressure, respectively. The fluid usually does not pass through an additional pressure hydraulic pump, in which deposits etc. may be formed.
The disadvantage with the previously-known ink jet printer resides in that, as the ink supply in the bag runs short, the print image deteriorates. There is a lack of simple evidence that the ink supply is running short. It is thus desired to provide an ink emptiness signal at the appropriate time.